Interaction of low-energy electrons with surface polarity near ferroelastic domain boundaries
Résumé
We derive surface polarity at and near ferroelastic domain boundaries from molecular dynamics simulations based on an ionic spring model. Interatomic gradient forces lead to flexoelectricity which, in turn, generates polarity at the surface and in twin boundaries. We then derive generic properties of electron scattering spectra equivalent to those observed in low-energy electron microscopy (LEEM) and mirror electron microscopy (MEM) experiments. Negatively (positively) charged surfaces reflect (attract) incident electrons with low kinetic energy. The electron images reveal the valley and ridge surface structures near the intersection of the twin boundary and the surface. Polarity in surface layers is predicted to be visible in LEEM and MEM spectra at neutral surfaces, but much less when surfaces are charged. Inward polarity reflects electrons similar to negative surface charges, and outward polarity backscatters electrons like positive surface charges. Both the polarity in the twin boundary and the physical topography scatter electrons, consistent with experimental LEEM and MEM experiments on CaTiO3 with (001) and (111) surface terminations.